Carl Icahn kicks Bill Ackman while he's down

The billionaire investor and founder of Icahn Enterprises decided on Thursday to dredge up one of his old feuds.

He told CNBC that Pershing Square's Bill Ackman was "dead wrong" in his short position in Herbalife, a multilevel marketing firm that sells nutritional supplements.

Of course, he also prefaced this by saying that Ackman was a "smart guy."

"Ackman is completely and totally wrong on this company," he said. "You know, Ackman is a smart guy and all, but he is just dead wrong. This company creates work for a lot of people. And to say it doesn't is ridiculous."

Herbalife's stock is up almost 110% since Bill Ackman declared before all of Wall Street in December 2012 that he had taken a short position against the company. It was just one of many positions that have turned against Ackman over the last year and change. In 2015, his hedge fund was down 20% for the year.

Ackman and Icahn have been feuding far longer than that, though. The two fell out over a deal (see: "schmuck insurance") after Ackman blew up his first hedge fund, Gotham Partners, in 2001. They sued each other for the next 10 years and, famously, couldn't even be in the same restaurant together.

Their feud ramped up again when Ackman started his crusade against Herbalife, which Ackman accused of being a pyramid scheme. He was very public about the position, giving multiple presentations slamming the company and kicking the whole thing off with a 342-slide deck at a special Sohn Conference event in New York City.

Icahn quickly took the other side of the trade, at one point calling Ackman a crybaby on CNBC:

"I'm telling you he's like a crybaby in the schoolyard. I went to a tough school in Queens, you know, and they used to beat up the little Jewish boys. He was like one of the little Jewish boys crying that the world is taking advantage of him."

To be fair, Icahn isn't having the greatest year either. In May, Standard & Poor's cut Icahn Enterprises' credit rating to junk. He's lost big on positions in energy stocks.

"We estimate that after quarter-end through May 13, 2016, IEP's large publicly traded positions declined by approximately $600 million, which would result in an LTV ratio of about 53%, holding all else equal," S&P's release said.